Principle

Formulas

Applying mesh analysis and Ohm’s law on the previous schematic highlights the direct link between the sensed tension (with A0 on the Arduino), the resistance variation of the sensor and thus the pressure applied on the sensor.

RC CIRCUIT

Demo

This program highlights RC circuit’s application.

By approaching the Capacitive Sensor with your hand, you see the led strip reacting in function of the distance to the sensor.

Experiences

Principle

The principle behind those Demo/Experimences are based on the capacitor charging/discharging phenoma of an RC circuit.

In the Experiences part we illustrated the capacitor discharge, here are the classical schematic and the formulas related to this circuit.

Following Vc over time reveals the characteristic equation of an RC circuit during the discharge

The time to load/unload the capacitor is directly related to the RC constant of the circuit.

By varying the distance between the 2 capacitive sensors, this modify the C constant which affects its load/unload time reaction.

In the Demo part, the interuptor is replaced by the pin 2 of the Arduino which simulate a square tension generator as you can use in the Experiences part.

Then the Arduino calculates the time to reach a significant tension value on its pin 4 and thus can give an estimation of C variations reflecting the distance variations between the 2 capacitive sensors.